It is known to use catalytic combustion in gas turbine engines to reduce NOx emissions. One such catalytic combustion technique known as lean catalytic, lean burn (LCL) combustion, involves completely mixing fuel and air to form a lean fuel mixture that is passed over a catalytically active surface prior to introduction into a downstream combustion zone. However, the LCL technique requires precise control of fuel and air volumes and may require the use of a complex preburner to bring the fuel/air mixture to lightoff conditions. An alternative catalytic combustion technique is the rich catalytic, lean burn (RCL) combustion process that includes mixing fuel with a first portion of air to form a rich fuel mixture. The rich fuel mixture is passed over a catalytic surface and mixed with a second portion of air in a downstream combustion zone to complete the combustion process.
U.S. Pat. No. 6,174,159 describes an RCL method and apparatus for a gas turbine engine having a catalytic combustor using a backside cooled design. The catalytic combustor includes a plurality of catalytic modules comprising multiple cooling conduits, such as tubes, coated on an outside diameter with a catalytic material and supported in the catalytic combustor. A portion of a fuel/oxidant mixture is passed over the catalyst coated cooling conduits and is oxidized, while simultaneously, a portion of the fuel/oxidant enters the multiple cooling conduits and cools the catalyst. The exothermally catalyzed fluid then exits the catalytic combustion system and is mixed with the cooling fluid outside the system, creating a heated, combustible mixture.
To reduce the complexity and maintenance costs associated with catalytic modules used in catalytic combustors, simplified designs are needed.